The present invention relates to a method and apparatus for remotely controlling a device, such as a toy, lock, smart card, or home appliance, via a control message that is imperceptibly embedded in an audio signal, e.g., as a xe2x80x9cwatermarkxe2x80x9d. Moreover, the invention optionally enables the device to be synchronized with the audio signal, for example, so that the actions of a doll can be synchronized with a children""s television program.
Audio signals are ubiquitous, being broadcast over AM/FM radio, TV, public announcement systems, transmitted over telephone channels, or stored on cassette tapes, CDs, computer memories, etc. Therefore, it is convenient to use audio channels or audio storage to transmit or store some other information.
Audio watermarking, or embedded signaling, has recently emerged as a technology for embedding auxiliary data imperceptibly in a host audio signal. A basic feature of audio watermarking techniques is that the embedded signal is substantially imperceptible to a listener of the host signal. Furthermore, the audio-watermarks occupy the same time/frequency/space domain as the host signal, so that they are not lost in standard audio signal processing, recording or transmissions, nor filtering and/or masking operations in a deliberate attack can remove them.
A primary proposed use of watermarking is in protecting intellectual property rights, e.g., through copy control, automatic broadcast monitoring, ownership dispute resolution, Internet commerce tracking, etc. Alternative applications include auxiliary data embedding, such as the song title and purchasing instructions, assurance of content integrity, proof of performance in TV and radio advertisements, audience exposure monitoring, caller identification (authentication) in telephone conversations, or generic covert communication.
Moreover, various schemes have been proposed for sending command and control signals, or their equivalent, concurrently with audio signals. However, these schemes do not qualify as audio watermarking techniques. For example, in one proposed scheme, an xe2x80x9cinstructional signalxe2x80x9d is inserted in a narrow frequency band set aside at the upper frequency edge of the audio spectrum. However, this system does not qualify as a watermarking system since the host and the control signals occupy distinct frequency bands.
In another proposed scheme, a unique code describing an offer for products and services is transmitted by a TV program as an audible xe2x80x9cbeepxe2x80x9d. There is no attempt to hide this beep, so this technique also is not audio watermarking.
In yet another proposed scheme, information related to a TV game show is encoded in touch tones and broadcast in-band with an audio portion of the show. The touch-tones can be masked by the show""s usual sound effects, such as buzzers and beeps. This is substantially different from the watermarking approach, because it cannot simultaneously meet the inaudibility requirement and the requirement for the time domain overlap of a watermark and an arbitrary audio signal.
Accordingly, it would be desirable to provide a watermarking system for sending command and control signals concurrently with audio signals that overcomes the disadvantages of the existing proposed schemes.
The system should use watermarking techniques to provide a hidden data channel in an audio signal for providing short messages, such as device activation commands, or remote control signals that can change the state of a device.
The system should be compatible with existing watermaking techniques, such as those disclosed in U.S. Pat. No. 5,940,135 to Petrovic at al., entitled xe2x80x9cApparatus and Method for Encoding and Decoding Information in Analog Signals,xe2x80x9d issued Aug. 17, 1999, and incorporated herein by reference.
The system should provide a hidden remote control signal as a watermark within an audio signal for controlling various devices that detect the hidden signal.
The system should allow the remote control signal to be related to, or independent of, content of the host audio signal. For related content, the system should optionally provide synchronization of the remote control signal with the host audio signal content.
The system should use a watermark to define a time gate (window) during which a device is enabled to receive a user input or perform a specified action.
The system should provide a security mechanism to ensure that the time gate is defined only from a real-time broadcast audio signal, and not from a replay of the audio signal.
The system should improve the robustness and temporal resolution of a watermark, and provide a simplified watermark detector.
The system should provide synchronization of a watermark encoder and decoder.
The present invention provides a system having the above and other advantages.
The present invention relates to a system for using a watermark embedded in an audio signal to remotely control a device.
In particular, the system is compatible with existing audio-watermarking technologies that use audio channels and/or audio storage to carry independent data without interfering with the audio channel""s original purpose. However, such a channel has much lower information capacity than a modem channel, typically no more than about twenty bits per second per audio channel. The invention uses this hidden data channel for relatively short messages, such as device activation commands, or remote control signals that can change state of a device.
A remote control signal is hidden within an audio signal that is broadcast over radio and TV, stored on CDs, DVD, tape or computer memory, played over speakers and/or transmitted over other audio channels. Various devices such as toys, computers, and appliances, that are equipped with an appropriate detector, detect the hidden signal to trigger an action, or change a state of the device. The device action can be completely unrelated to the ongoing audio content, and it can have a number of different objectives, such as entertainment, education, sales, security, etc.
In one particular implementation, a xe2x80x9ctime gatexe2x80x9d device is disclosed, where detection of the watermark opens a time interval within which a user is allowed to perform an action, such as pressing a button, typing in an answer, turning a key in a lock, etc. To prevent fraudulent activation of a time gate, the time gate device can be further upgraded to react only to watermarks coming from live broadcasts, and not from replays from tapes or other storage devices.
In another implementation, detection of the watermark triggers an action.
Additionally, techniques are presented for improving existing watermarking technology in view of requirements for the proposed applications. In particular, the invention provides improvements in robustness of the watermark in the channels with acoustic propagation (e.g., propagation through air)xe2x80x94using delay hopping (watermarking adjacent bits using distinct autocorrelation delays), robustness improvements using redundant watermarking, improvements in the time resolution of the trigger feature, and simplifications of the detector design.